1. Field of the Invention
The present invention relates to a discharging head and a liquid discharging apparatus, and particularly, to a liquid discharging head for discharging liquid droplets by means of energy generated by an actuator.
2. Description of the Related Art
Recently, inkjet recording apparatuses (inkjet printers) have become common as recording apparatuses for printing and recording images captured by digital still cameras, and the like. An inkjet recording apparatus comprises a plurality of nozzles (recording elements) in a head, the recording head being scanned while droplets of ink are discharged onto a recording medium from the nozzles, the recording medium being conveyed through a distance corresponding to one line, each time one line of an image is recorded onto recording paper, and an image being formed onto the recording paper by repeating this process.
Inkjet printers include those which use a fixed-length serial head, and carry out recording by scanning the head in the lateral direction of a recording medium, and those which use a line head in which recording elements are arrayed over a length corresponding to the full dimension of one edge of the recording medium. In a printer using a line head, it is possible to record an image across the entire surface of the recording medium, by scanning the recording medium in an orthogonal direction to the direction in which the recording elements are arranged. In a printer using a line head, it is not necessary to provide a conveyance system, such as a carriage, for scanning a short-dimension head, nor is it necessary to move a carriage, or perform complicated scanning control of the recording medium. Furthermore, since only the recording medium is moved, it is possible to increase the recording speed in comparison to printers using serial heads.
Ink chambers (or pressure chambers) for storing ink to be discharged are provided respectively at the plurality of nozzles discharging ink, and these ink chambers are connected respectively to the nozzles. When pressure is applied to the ink inside an ink chamber, ink is discharged from the corresponding nozzle.
Pressure may be applied to the ink by means of a thermal jet method, wherein the ink is heated by providing a heat source in each ink chamber, a bubble is created due to this heat, and this bubble pressurizes the ink inside the ink chamber, or by means of piezoelectric method, wherein a piezoelectric element is provided on the wall of each ink chamber, the wall of the ink chamber is pressurized by displacement of this piezoelectric element, and the ink inside the ink chamber is discharged due to this pressure.
In the piezoelectric method described above, various ways have been devised for efficiently transmitting the energy of the piezoelectric element to the ink inside the ink chamber.
Japanese Patent Application Publication No. 63-57250 discloses an inkjet head having a structure where grooves for concentrating the distortion energy are provided on a vibration plate which vibrates due to the distorting effect of drive elements. These grooves are formed on the surface of the vibration plate where the drive elements are installed, or on the surface which opposes the ink chambers. Thereby, the ink droplet ejection efficiency is improved, without having to increase the drive voltage applied to the drive elements or reduce the thickness of the vibration plate. Furthermore, vibrations generated in the ink chambers during driving are prevented from affecting adjacent ink chambers, which are not being driven.
Japanese Patent Application Publication No. 11-300971 discloses an inkjet recording head and an inkjet recording apparatus, wherein a vibration plate forms a portion of a pressure generating chamber connected to a nozzle opening, and this vibration plate contains a recess situated in a portion of the inner side of the pressure generating chamber. Thereby, initial variations in the vibration plate are suppressed.
Japanese Patent Application Publication No. 11-309864 discloses an inkjet recording head and an inkjet recording apparatus, wherein a vibration plate forms a portion of a pressure generating chamber connected to a nozzle opening. This vibration plate contains recesses extending longitudinally along the inner sides of the pressure generating chamber, and these recesses are situated on at least either side in the lateral direction of the chamber. Thereby, the displacement generated by driving the piezoelectric actuator unit is increased.
Furthermore, Japanese Patent Application Publication No. 2002-225264 discloses an inkjet printer head and a piezoelectric/electrostrictive actuator for an inkjet printer head, wherein a recess is formed in a vibration transmitting plate forming a wall of a pressure chamber, the recess being of reduced rigidity. Thereby, a structure is achieved wherein the perimeter region of the vibration transmitting plate also contributes to producing displacement.
However, if the voltage applied to the piezoelectric elements is set to a high voltage in order to increase the displacement of the piezoelectric elements, then the size of the power source supplying voltage to the piezoelectric elements must be increased, and furthermore, protective circuits, and the like, must be provided, in order to handle the high voltage. Moreover, the vibration plate which is pressurized by the piezoelectric elements loses strength if it is reduced in thickness. Therefore, cross-talk between adjacent ink chambers is more liable to occur. In addition, the manufacturing processes required to produce a vibration plate of reduced thickness are complicated, and such a plate is difficult to manufacture.
In the inkjet head according to Japanese Patent Application Publication No. 63-57250, there is no disclosure regarding the positioning of the grooves provided in the vibration plate, or the shape of these grooves.
Furthermore, in the inkjet recording head and inkjet recording apparatus according to Japanese Patent Application Publications Nos. 11-300971 and 11-309864, recesses provided in the longitudinal direction are disclosed, but the beneficial effect of such recesses is limited to pressure generating chambers having a rectangular or diamond shape.
Furthermore, in the inkjet printer head and piezoelectric/electrostrictive actuator for an inkjet printer head according to Japanese Patent Application Publication No. 2002-255264, some beneficial effect is obtained in terms of increasing displacement, but beneficial effects in reducing cross-talk and stabilizing bonding are not readily achieved.